[Sigia-l] research: when is it enough?

[PeterV]

Hi all,
when doing user research (of any type), when do you know you have enough? 
Apart from the fact that you probably rarely have enough time for research, 
how do you decide: now it's enough and time for something else?
One answer: when you start hearing the same things again and again.

A related question: how can you know how much research you'll need 
beforehand, ie. when planning or selling the research. I've found that hard 
in practice. Any insights?
Thanks,
PeterV
http://petervandijck.net